Colloidal sols of dispersed particles such as metals, semiconductors, polymers, have attracted considerable interest due to their photochemical, photocatalytic, and photovoltaic properties or to their optical non-linearities, see Takami A. et al., Jpn. J. Appl. Phys., 35:L781, (1996).
For silver, there has been interested in investigating its optical properties since it strongly absorbs in the visible region due to plasmon resonance. Also, silver has long been known as an antiseptic with the power to kill bacteria and other germs. Ancient Greeks and Romans kept their liquid free of contamination by placing them in silver jars. In a study done, in part, by the institute of Microbiology in Rome, Italy, and published in xe2x80x9cApplied and Environmental Microbiologyxe2x80x9d, in December, 1992, various forms of silver were tested for their ability to kill microorganisms. Silver particles are 100 times more effective than silver salts as antiseptics. Thus, it is important to prepare nano-sized silver particles or silver alloyed particles to maximize the performance of silver in killing microorganisms. Conventionally, silver nanoparticles have been prepared by various methods such as co-precipitation methods in aqueous solutions, electrochemical methods, aerosol, reverse microemulsion, chemical liquid deposition, photochemical reduction, chemical reduction in solution and UV irradiation. But all of these methods have limitations in controlling the particle size and production of particles on an industrial scale. To overcome these limitations, recently, surfactants have been used (WO 99/43427).
It is well known that surfactants provide several types of well-organized assemblies, which provide the specific size, geometry and stabilization to particulate assemblies formed within the organized surfactant assemblies. Table I shows some of the conventionally used host surfactant assemblies that are available for the formation of nanoparticle species which include aqueous micellar solution, reverse micelle, microemulsion, vesicle, monolayer, Langmuir-Blodgett films and bilayer lipid membranes (Dixit et al., Colloids and Surfaces A: Engineering and Physico-Chemical Aspects, 133:69 (1998)).
In this invention, we describe the preparation of nanoparticles of silver and silver alloyed with other elements such as platinum (Pt), palladium (Pd), gold (Au), aluminum (Al), cadmium (Cd) and sulfur (S) in aqueous surfactant solutions. Depending on the nature of the prepared materials, two types of adsorption may be considered: hydrophobic portions will bind hydrophobically with other hydrophobic parts of the surfactant, and in the same way, hydrophilic portions will bind hydrophilically with the other hydrophilic parts of the surfactant.
Furthermore, two kinds of binding behavior can be observed according to the surface charge of the particles and surfactant head groups. In one case, if the ionic surfactant has an opposite charge to the particle, the hydrophilic head groups of the surfactant bind to the particle, wherein the particle becomes hydrophobic. This type of a surfactant-covered particle cannot be kept in an aqueous environment, unless a double-layer of surfactant molecules is formed. However, this is difficult to achieve with very small colloidal particles. In the second case, if the ionic surfactant head group has the same charge as the particle surface, the binding of the surfactant head groups does not occur. Thus, the type of ionic charge of the head groups in surfactant molecules is very important in relation to the adsorptive ability of the surfactant to bind to the particle surface, and affects the size of the particles formed in surfactant solutions. Due to the above-mentioned mechanism, the kind of hydrophilic group in surfactant influences the particle size formed in surfactant solutions. Thus, there is a need in the art to efficiently produce silver containing nanoparticles by using a simple method.
The present invention has met the herein before described need.
It is an object of the present invention to provide a simple preparation method for silver and silver alloyed nanoparticles having a well-controlled size in a surfactant solution. It is a further objective of this invention to provide an economic and simple preparation method for silver alloyed with other inorganic elements such as Pt, Pd, Au, Al or S to modify the physico-chemical properties of silver nanoparticles in a surfactant solution.
The procedure for the formation of size-controlled silver nanoparticles in surfactant solutions can be described as follows: (step 1) prepare an aqueous silver salt solution such as silver nitrate, silver acetate or other water soluble silver salts, (step 2) prepare an aqueous solution of a reducing agent of silver ions and surfactant, and (step 3) adding the solution prepared in step 2 into the solution prepared in step 1, or vice versa to form a silver colloid.
For the formation of alloyed silver nanoparticles, a mixed water-soluble salts solution of silver and water-soluble salt is prepared, which can bring together the wanted ions in the same manner as in the above-mentioned step 1. Metals such as palladium nitrate for Agxe2x80x94Pd alloyed nanoparticles, HAuCl4 for Agxe2x80x94Au alloyed nanoparticles, and so can be used. For example, the alloyed nanoparticles of silver and palladium can be prepared by mixing a mixed salt solution of silver nitrate and palladium nitrate and adding the aqueous solution of the reducing agent and the surfactant into this solution. Nanoparticles of Ag/Pd alloy are then obtained. In this case, the physico-chemical properties of the particles would be different from those of silver and palladium nanoparticles. The size of the alloyed nanoparticles depends on the kind and/or concentration of surfactant used, similar to the procedure used in the formation of silver nanoparticles.
For the formation of Ag/Au alloyed nanoparticles, silver nitrate and HAuCl4 are dissolved in water at a desired ratio. The aqueous solution of reducing agent such as hydrazine, ethylene glycol, ethylene oxide based chemicals, NaBH4, LiBH4, or LiAlH4 and surfactant are added into a mixed salt solution while stirring. Thus, an alloyed Ag/Au nanoparticles can be obtained.
The size of the nanoparticles can be adjusted by changing the type of the surfactant or the concentration of the surfactant in an aqueous solution. For the silver and alloyed silver nanoparticles, anionic and nonionic surfactants produced fine particles, but the cationic surfactant was not as efficient as anionic or nonionic surfactants possibly due to the positive surface charge of silver particles in aqueous solution.
It is an object of the invention to provide a method for making a nano-sized silver particle comprising:
(i) preparing an aqueous silver salt solution;
(ii) preparing an aqueous solution comprising a silver ion reducing agent;
(iii) preparing an anionic, nonionic or amphoteric surfactant solution, or a mixture thereof; and
(iv) mixing the solutions prepared in steps (i-iii) in any order to form a nano-sized silver particle, wherein the solutions are prepared together or separately.
The surfactant may be present in 0.01-10 weight % when the solutions prepared in steps (i-iii) are combined. The anionic surfactant may include sodium dodecyl sulfate or sodium decyl sulfate. The nonionic surfactant may include an ethylene oxide, alkyl(poly) glucoside or alkylglycerol ether. The amphoteric surfactant may include dodecyl amine oxide and decyl amine oxide. All surfactants comprise 8-12 carbon atoms in the hydrophobic part of the surfactant.
The reducing agent used may be hydrazine, NaBH4, LiBH4, LiAlH4, ethylene glycol, an ethylene oxide based chemical, or an alcohol. And the nano-sized particle may have a diameter of below 200 nanometers or may have a diameter of less than 20 nanometers.
The present invention is also directed to a method for making a nano-sized silver alloyed particle comprising:
(i) preparing separately or together an aqueous silver salt solution and an aqueous inorganic element salt solution, wherein said inorganic element is other than silver;
(ii) preparing separately or together an aqueous solution comprising a silver ion reducing agent and an aqueous solution comprising an inorganic element ion reducing agent;
(iii) preparing an anionic, nonionic or amphoteric surfactant solution or a mixture thereof; and
(iv) mixing the solutions prepared in steps (i-iii) in any order to form a nano-sized particle of silver alloyed with said inorganic element, wherein the solutions are prepared together or separately.
It will be seen that the nanoparticle prepared using the method of the invention may be used for a variety of situation and purposes, some of which are detailed here. For example, an object of the invention is to provide a method for disinfecting or sterilizing a substrate comprising administering to the substrate an effective amount of the nano-sized particle that is obtained using the method according to the invention. Other uses for the nano-sized particle made using the method of the invention include: catalyzing a chemical reaction comprising administering to the reaction an effective amount of the nano-sized particle; chemically or mechanically polishing a surface comprising administering to the surface an effective amount of the nano-sized particle; removing static charge from a substrate, comprising administering to the substrate an effective amount of the nano-sized particle; enhancing electroconductivity in electroconducting materials, comprising administering to the materials an effective amount of the nano-sized particle; and shielding a substrate from the effects of electromagnetic wave, comprising administering to the substrate an effective amount of the nano-sized particle; and enhancing photo-response of a substrate comprising administering to the substrate an effective amount of the nano-sized particle.
In another embodiment, the present invention is directed to a method for preventing oxidation of a substrate comprising administering to the substrate an effective amount of the nano-sized particle together with an anti-oxidant. The anti-oxidant may be butylhydroxy toluene or a vitamin E derivatives, among others, and may be useful for enhancing the health of an individual to ingests the nanoparticle with an anti-oxidant.
These and other objects of the invention will be more fully understood from the following description of the invention, the referenced drawings attached hereto and the claims appended hereto.